A One Chip, Polysiiicon, Surface Micromachined Pressure Sensor with Integrated CMOS Signal Conditioning Electronics

In this paper the integration of a polysiiicon, surface micromachined, absolute pressure sensor with analog CMOS (Complementary Metal Oxide Semiconductor) signal conditioning circuitry is a cavity filled with sacrificial oxide. The evacuated cavity under the polysiiicon plate is created by removing the sacrificial oxide and sealed using reactive sealing. The pressure is sensed by a Wheatstone bridge formed from dielectrically isolated polysiiicon piezoresistors deposited on top of the polysiiicon diaphragm [4].

The integrated sensor chip is formed by interweaving a standard CMOS process with the sensor fabrication processes. All of the sensor process steps are compatible with standard CMOS processing A total of 17 mask steps is required for both the sensor and the signal conditioning electronics, including a passivation layer over the CMOS electronics. The sensor and the signal conditioning electronics have been fabricated on a prototype die measuring 2.54 mm on a side. A production die 1.78 mm on a side is in wafer fabrication.

The signal conditioning electronics amplifies and temperature compensates the sensor bridge output. The output of the sensor is ratiometric and can drive a IK Ohm load to within 200 mV of either power supply rail. The chip requires a 5V regulated supply. The temperature compensation reduces the temperature error to less than 2.5% of Vref over a temperature range of −40 to 150 °C. Polysiiicon thin film resistors are laser trimmed to adjust offset and gain of the signal conditioning electronics.

Absolute pressure sensors have been fabricated in pressure ranges from 0-to-450 KPa up to 0-to-17 MPa. Performance data over temperature for various pressure ranges is presented and results of overpressure and pressure cycling tests are shown.